1. Field of the Invention
This invention relates to improvements in the compositions of a photographic color forming agent for processing a silver halide color photographic light-sensitive material and, more particularly to the compositions of a photographic color forming agent capable of preventing a harmful action caused by intermixed heavy metal ions.
2. Description of the Prior Art
Generally speaking, a silver halide color photographic light-sensitive material produces a dye image in a series of photographic processes fundamentally comprising a process of exposing imagewise to light, a color development process and a desilvering process.
In the above-mentioned color development process, a dye image with an image pattern is formed by a coupling reaction of the oxidants of a color developing agent with coexisting color couplers and at the same time reduced silver is produced. In the next desilvering process, the silver produced thereby is oxidized with a bleaching agent and is then changed into a soluble silver complex by a reaction with a fixer and is finally removed by dissolving it in washing water.
On the other hand, in an ordinary type of color developing liquids, a sulfite or a water-soluble salt of sulfite and hydroxylamine is added thereto to serve as a preserving agent so as to prevent the aromatic primary amine color developing agent from being oxidized.
It has already been known that, if only a sulfite is added to a developer independently, the satisfactory preservability is not always expected and more effective preservability can be obtained by adding hydroxylamine in the form of a water soluble salt. Besides the above, it has also been known that dihydroxyacetone, anilino ethanol, hydroxyl urea and the like can serve as such preserving agents, in place of the described hydroxylamine and a sulfite.
It is known that the preservation effects of these preserving agents are declined by the oxidation thereof caused by a catalysis with a very small amount of co-existing metal ions such as iron ions in particular, and that fog or stain is produced on a color photographic light-sensitive material because the described hydroxylamine salt is apt to produce ammonia and resultantly that the photographic characteristics are changed.
To prevent such unfavorable actions of the metal ions, the techniques of containing a variety of metal chelating agents have been proposed and put in practical application. For example, there may be given a technique disclosed in U.S. Pat. No. 3,839,045 wherein a hydroxyalkylidene-diphosphonic acid metal ion chelating agent and a lithium salt are used in combination; a technique disclosed in U.S. Pat. No. 3,746,544 wherein a polyhydroxy compound and an aminopolycarboxylic acid metal ion chelating agent are used in combination; a technique disclosed in U.S. Pat. No. 4,264,716, wherein a polyhydroxy compound and an aminopolyphosphonic acid metal ion chelating agent are used in combination; and the like. According to these techniques, it is possible to reduce the influences of a heavy metal ions such as iron ions mixed in a developing liquid.
From the results of the studies by the inventors of this invention, it was found that a photographic light-sensitive material caused fogs thereon and the photographic characteristics thereof became abnormal in which the shoulder in particular showed a hard contrast even if the described chelating agents were added, when a continuous process was carried out with an automatic processing machine. Particularly in both of a low replenishment process capable of economizing the quantity of replenishers used and a regenerative process capable of reusing an overflow both with the purposes of controlling pollutions and conserving natural resources, each process is a high-light of the modern photographic processes, it was recognized that the above-mentioned abnormality in the photographic characteristics is getting more serious as heavy metal ions are accumulated.
After the inventors devoted themselves to try to locate the causes of the findings, they finally located the following. Only the iron ions mixed in as an impurity have so far been discussed as the causal material of the above-mentioned phenomena, and it was however located that not only the described iron ions but the increase of copper ions mixed in also causes the described abnormality in photographic characteristics, and it was further found that any conventional chelating agent or any combination thereof can hardly be effective against copper ions and is also hard to make such copper ions harmless. To be concrete, a color developing liquid being popularly used contains copper ions of at least 0.1 ppm. and, ordinarily, nearly 0.3 ppm. Hydroxyalkylidene-diphosphonic acid metal ion chelating agent which is a conventional chelating agent used in a color developing liquid is not effective at all on copper ions, and a combination of a polyhydroxy compound and an aminopolycarboxylic acid metal ion chelating agent having not less than three carboxy groups disclosed in the aforementioned U.S. Pat. No. 3,746,544 cannot completely prevent any catalysis of copper ions. In addition to the above, there are some instances where a decomposition of hydroxylamine which is a preserving agent is accelerated thereby. Resultantly, the photographic characteristics of a processed photographic light-sensitive material will become abnormal, that is also a fault. A combination of a polyhydroxy compound and aminopolyphosphonic acid metal ion chlating agent has such a fault as is hard to put it in practical use because it precipitates with calcium ions, though it can cover heavy metals.